Evening star. [volume] (Washington, D.C.) 1854-1972, 1887-05-07

learned from the stars how It is recorded and how
communicated to the world. There are many
little calculations however, to be made each day
For instance, there are errors Of the clock. Tht
entirely provided for by the Commensurate ren
dulum, SO combined of steel and mercury that th,
center OF gravity constantly shirts with change:
lated ana arranged so as to keep the pendulum
swinging at the same rate Atmosphertc chanres
however, cannot be anticipated in this way. ant
II there Is high barometer the clock win 81
slow, and If there is a low barometer
officers to THE STAR reporter. :the pentulum vii
swing faster through light orrarfflad atmosphert
than !, through ron dense and heavy one, because
unnoticed In an ordinary time piece. hut I'm ciocS
that Is compared daily with the stars it becomes
SppRations Of on cg great
second q day have been noticed.
THE personal EQUATION
Then there Is the personal euuat1onn OF the oh.
server to be considered. That Ia thing that de.
ponds upon his nervous and muscular constitu.
ton; Between the time the star appears on the
passage is recorded on the chronorranh an i'm.
preston has to be made on the mind of the obsery.
er through his eye, the mind has to send out its
command to the hand on the telegraph key. and
the hand has to execute it. The spersonal eaua-
tom Is the length OF time required for this mental
and manual action. When new observer comes
In course OF time its amount is established and ii
always becomes factor in the calculations. In
experienced observers though sometimes the s.per-
Sonal equation" amounts to as much as q second.
the amount never varies.
In sQch minute calculations there is another fac.
COr. The meridian for which the time is recorded
IS that which passes through the center of the
dome OF the observatory. The transit Instrument
Is locateo ABOUT twenty PAGES to the east. The
Cme taken the sun or star to pass over this space
mas 10 De considered. This amounts to about two
nundreotnS or second. All OF these things are
inquired OUT and then the astronomer is able TO get
at tne error or his clock and establish its s.raten
THE SHIPS CHRONoMETKKs.
The Naval Observatory not only finds out the
time and apprises the world, but it does up time,
SO to speak, In snug packages for use on ship
board. The ships chronometer is as important to
the navigator as his compass or his rudder. In
the CLOCK room at the Observatory Is huge case
containing rows and rows OF ships chronometers'
Every new chrOnometer for the Navy and every
Old chronometer, upon Its return from cruise,
goes TO the Observatory to take course OF train.
ing there and have It's "rate" established Each
one becomes study. Its variations under differ
ent conditions OF temperature is noted and finally
It's curve 1s ''platted." That is, chart or dia-
gram is made, with curving line running through
pected OF the chronOmeter under any given condi-
lions OF temperature. The navigator never at
tempts to set his chronOmeter right. All he wants
to know is its rate, and he can then figure out the
truth. Thus these little clocks come regularly to
SIT at the feet OF the great clock oracle TO imbbe
its wisdom, and to have their own Inconsistency
measured.